This invention relates to a process and apparatus for controlling gasket force in an electrolysis cell.
Electrolytic cells, particularly of the filter press-type, used for the electrolysis of aqueous salt solutions are well known and have been commercially employed for the production of chlorine and caustic from brine. Filter press-type electrolytic cells commonly employ a plurality of frames having electrodes held thereto and assembled in filter press type arrangement, separated from each other by membranes, diaphragms or microporous separators, forming a plurality of anolyte and catholyte compartments. The separators used in filter press-type cells are generally in sheet form and have ion exchange properties. The electrodes used in the cells are generally monopolar or bipolar electrodes.
Typically, a press means such as a hydraulic squeezer unit is used to compress or clamp together the separators in sheet form between the sides of the frame members to form a filter press cell electrolyzer unit. The anolyte and catholyte compartments of the cell are then filled with electrolyte.
Typically, to provide a fluid-tight seal between the frame members of the cell and the separator without damaging the separator, substantially flat, solid gaskets having a rectangular cross sectional area or tubular type gaskets having a circular cross sectional area made of elastomeric materials are disposed between the peripheral flange of the frame members and the separator. One or two gaskets can be installed between the cell frame members on either side of the membrane.
Using the squeezer apparatus such as the hydraulic unit, a set squeeze pressure load on the gaskets is used to obtain a fluid-tight seal in the cells. After operation, if the cells require an additional squeeze pressure to seal the cells, the squeeze pressure is adjusted manually and the cells are squeezed tighter. Oversqueezing the gaskets is a potential problem with increased gasket loads which, in turn, may cause damage to the membrane by thinning of the membrane and subsequent rupture and/or perforation at the thinned area at the edge of the gasket.
When cells run at atmospheric conditions, manual adjustments to the squeeze load on the gaskets are satisfactory because no internal force which opposes the squeeze force is present within the cells. When pressurized cells are used, however, adjusting the squeeze pressure to the right setting to prevent over squeezing the gaskets and damage to the membranes is more critical, particularly when a process upset occurs during operation of the cells. For example, during operation of the cells, if there is a gasket failure and a leak occurs in one compartment there can be a pressure loss in the overall cell structure. If such a pressure loss occurs and there is no system which adjusts to the pressure loss, an excess pressure will be placed on the gaskets. The pressure on the gaskets will, in turn, transfer to the membrane resulting in tearing of the membrane. Membrane tears inevitably lead to a shutdown of the cell operation. Relatively expensive chlorine cell membranes are ruined by application of excessive gasket pressure.
What is needed, therefore, is an automatic control system to balance pressure during operational upsets, startups and shutdowns of the cells. It is desired therefore, to provide a system and process which controls the gasket pressure at a preset value and minimizes membrane damage.